Sheet transport and registration apparatus

ABSTRACT

An apparatus in which a sheet is registered during the movement thereof. The sheet is moved along a path in a forward direction of movement and a lateral direction of movement substantially normal thereto. The lateral movement of the sheet causes the side edge of the sheet to engage a registration edge so as to be aligned thereat. The magnitude of the moving force applied on the sheet is proportional to the thickness of the sheet. In this way, the moving force varies as a function of the thickness of the sheet with the sheet slipping laterally when engaging the registration edge to prevent buckling thereof.

This invention relates generally to an electrophotographic printingmachine, and more particularly concerns an apparatus for registering asheet during the movement thereof.

In a typical electrophotographic printing process, a photoconductivemember is charged to a substantially uniform potential so as tosensitize the surface thereof. The charged portion of thephotoconductive member is exposed to a light image of an originaldocument being reproduced. Exposure of the charged photoconductivemember selectively dissipates the charges thereon in the irradiatedareas. This records an electrostatic latent image on the photoconductivemember corresponding to the informational areas contained within theoriginal document. After the electrostatic latent image is recorded onthe photoconductive member, the latent image is developed by bringing adeveloper material into contact therewith. Generally, the developermaterial comprises toner particles adhering triboelectrically to carriergranules. The toner particles are attracted from the carrier granules tothe latent image forming a toner powder image on the photoconductivemember. The toner powder image is then transferred from thephotoconductive member to a copy sheet. The toner particles are heatedto permanently affix the powder image to the copy sheet.

In a commercial printing machine of the foregoing type, the copy sheet,with the information permanently reproduced thereon, is transported to acompiler which collects sheets to form document sets. As the sheets aretransported to the compiler, the side edges thereof are registered. Atthe compiler, the sheets are attached to one another to form thedocument set. The sheets may be attached to one another by either astapler or a binder. The document set is then ejected at a high speedfrom the compiler into a catch tray for subsequent removal therefrom. Ina typical registration transport, a force is applied on the copy sheetsto move them to a fixed registration edge as the sheets aresimultaneously moved towards an exit. The driving force is normallyfurnished by a driver which is slightly angled toward the registrationedge. This driver is usually an angled ball on a belt, pinch roll, orany other similar device. With any type of mechanism, the driving forcemust be designed such that when the copy sheet engages the registrationedge, it can slip in the drive nip before it buckles. However, as thesheet slips, it must also continue to move forward toward the exit ofthe transport. In such transports, there is a delicate balance of forceswhenever a wide range of sheet weights must be handled. When lightweight sheets are being fed, a low drive force is required to avoidbuckling the sheet when it engages the registration edge. When heavierweight sheets are used, a higher driving force is required to overcomethe drag caused by sheet curl. There have been various attempts made todesign a system that automatically adjusts the drive force as a functionof sheet thickness. These systems may be effective, but the initial setup is critical and the system is susceptible to wear and partstolerances.

Various approaches have been devised for registering a copy sheet duringthe movement thereof. The following disclosures appear to be relevant:

U.S. Pat. No. 2,995,364. Patentee: Frederick et al. Issued: Aug. 8,1961.

U.S. Pat. No. 3,148,877. Patentee: Brearley. Issued Sept. 15, 1964.

U.S. Pat. No. 3,595,565. Patentee: Bergland. Issued: July 27, 1971.

U.S. Pat. No. 3,762,700. Patentee: Peterson et al. Issued: Oct. 2, 1973.

U.S. Pat. No. 3,989,237. Patentee: Goff, Jr. et al. Issued: Nov. 2,1976.

U.S. Pat. No. 4,179,117. Patentee: Rhodes, Jr. Issued: Dec. 18, 1979.

U.S. Pat. No. 4,193,590. Patentee: Mongagnino. Issued: Mar. 18, 1980.

U.S. Pat. No. 4,305,577. Patentee: Clay, et al. Issued: Dec. 15, 1981.

U.S. Pat. No. 4,579,444. Patentee: Pinckney et al. Issued: Apr. 1, 1986.

The relevant portions of the foregoing patents may be summarized asfollows:

Frederick et al. describes an apparatus for feeding bank checks ofdifferent thicknesses in which sets of rollers are placed tangential tothe path of travel of individual checks. Each set of rollers is placedat a different angle with respect to an edge guide to sequentially feedthe checks toward the guide.

Brearley discloses a sheet driving and aligning mechanism using aplurality of thin wafer-like rolls or disks spaced along a desired feedpath for successive sheets. A freely rotatably idler roller is mountedbelow and in vertical alignment with each disk to provide a sheetgripping bite into which successive sheets are advanceable. The aligningcomponent of force varies according to the stiffness of the materialfrom which the disks are made. The greater the stiffness, the greaterthe force. If exceptionally thin and light weight sheets are beingdriven and aligned, the disks should be formed of a material which isquite flexible to keep the aligning component of the force at anabsolute minimum and prevent edge damage to the sheets.

Bergland teaches the use of belts for advancing and urging sheets towardan edge guide. The belts engage opposite sides of the sheet. A slightcorrugation of the sheets is temporarily formed in the longitudinaldirection of sheet motion.

Paterson et al. describes a device for feeding and aligning documents.The documents are supported on a platform. A feed belt is positioned ina channel in the platform. Movable spheres are arranged to press againstone surface of the belt. A roller having a portion thereof extendingthrough a slot in the platform is adapted to engage one side of thedocument supported on the belt. The spheres engage the other side of thedocument pressing it against the belt. When the spheres engage thedocument, the document moves with the belt. When the spheres are nolonger pressed against the document, the document is driven by theroller against an edge guide.

Goff, Jr. et al. discloses a method for separating a top sheet from astack of sheets by causing the top sheet to buckle slightly due to alaterally applied force. Thereafter, a lateral force is applied in theopposite direction to remove the sheet.

Rhodes, Jr. describes a set of drive and alignment rollers for use in acopier. The drive roller is skewed relative to the path of travel withthe alignment roller being skewed in an opposite direction. In this way,the copy sheets are moved towards a reference edge.

Mongagnino discloses an adjustable feed deck having a multiple positionsetting to provide inter batch changes between a separator and a rollerto feed sheets of varying thickness.

Clay, et al. describes a shingle or wheel-type document feeder which hasan arm to apply a force normal to the shingle or wheel to thereby stackthe documents.

Pinckney et al. discloses a document side edge registration anddeskewing system including a deskewing drive roller and its matingdeskewing idler roller. Take away rolls are aligned to the document pathso as to feed the document sheet through arcuate document guides orbaffles. After the lead edge of the document has entered the nip betweenthe deskewing rollers, a solenoid separates the take away rollsreleasing the document so that the deskewing rollers can advance thedocument against a registration edge.

In accordance with one aspect of the present invention, there isprovided an apparatus for registering a sheet during the movementthereof. The apparatus includes a registration edge. Means move thesheet along a predetermined path having a forward direction of movementand a lateral direction of movement substantially normal to the forwarddirection of movement. The lateral movement of the sheet causes the sideedge of the sheet to engage the registration edge so as to be alignedthereat. The moving means applied a moving force having a magnitudeproportional to the thickness of the sheet so that the moving forcevaries as a function of the thickness of the sheet being moved with thesheet slipping laterally when engaging the registration edge to preventbuckling thereof.

Pursuant to another aspect of the features of the present invention,there is provided an electrophotographic printing machine of the typehaving a document handling apparatus for advancing individual documentsheets from a stack to an exposure station and returning to the stack inrepeated cycles. A processor forms copies of the documents. Each copysheet is advanced to a copy sheet attaching station and registeredduring the movement thereof. The improvement in the printing machineincludes a registration edge, and means for moving the copy sheet alonga predetermined path having a forward direction and a lateral directionof movement substantially normal to the forward direction of movement.The lateral movement of the copy sheet causes the side edge of the copysheet to engage the registration edge so as to aligned thereat. Themoving means applies a moving force having a magnitude proportional tothe thickness of the copy sheet so that the moving force varies as afunction of the thickness sheet being moved with the copy sheet slippinglaterally when engaging the registration edge to prevent bucklingthereof.

Other aspects of the present invention will become apparent as thefollowing description proceeds and upon reference to the drawings inwhich:

FIG. 1 is a schematic elevational view depicting an illustrativeelectrophotographic printing machine incorporating the sheet transportand registration apparatus of the present invention therein;

FIG. 2 is a schematic elevational view showing the FIG. 1 sheettransport and registration apparatus;

FIG. 3 is a fragmentary sectional elevational view taken along the line3--3 of FIG. 2 showing the sheet transport and registration apparatus;and

FIG. 4 is a top elevational view showing the orientation of the rollersof the FIG. 2 sheet transport and registration apparatus.

While the present invention will hereinafter be described in connectionwith a preferred embodiment thereof, it will be understood that it isnot intended to limit the invention to that embodiment. On the contrary,it is intended to cover all alternatives, modifications, andequivalents, as may be included within the spirit and scope of theinvention as defined by the appended claims.

For a general understanding of the features of the present invention,reference is made to the drawings. In the drawings, like referencenumerals have been used to identify identical elements. FIG. 1schematically depicts an electrophotographic printing machineincorporating the features of the present invention therein. It willbecome evident from the following discussion that the sheet transportand registration apparatus of the present invention may be employed in awide variety of devices and is not specifically limited in itsapplication to the particular embodiment depicted herein.

Referring to FIG. 1 of the drawings, the electrophotographic printingmachine employs a belt 10 having a photoconductive surface 12 depositedon a conductive substrate 14. Preferably, photoconductive surface 12 ismade from a selenium alloy with conductive substrate 14 being made froman aluminum alloy. Other suitable photoconductive materials andconductive substrates may also be employed. Belt 10 moves in thedirection of arrow 16 to advance successive portions of photoconductivesurface 12 sequentially through the various processing stations disposedabout the path of movement thereof. Belt 10 is entrained about strippingroller 18, tensioning roller 20, and drive roller 22. Stripping roller18 is mounted rotatably so as to rotate with belt 10. Tensioning roller20 is resiliently urged against belt 10 to maintain belt 10 under thedesired tension. Drive roller 22 is rotated by motor 24 coupled theretoby suitable means such as a belt drive. As roller 22 rotates, itadvances belt 10 in the direction of arrow 16.

Initially, a portion of photoconductive surface 12 passes throughchanging station A. At charging station A, a corona generating device,indicated generally by the reference 26 charges photoconductive surface12 to a relatively high, substantially uniform potential.

Next, the charged portion of photoconductive surface 12 is advancedthrough imaging station B. At imaging station B, a document handlingunit, indicated generally by the reference numeral 28, is positionedover platen 30 of the printing machine. Document handling unit 28sequentially feeds documents from a stack of documents placed by theoperator face up in a normal forward collated order in the documentstacking and holding tray. A document feeder located below the trayforwards the bottom document in the stack to a pair of take-awayrollers. The bottom sheet is then fed by the rollers through a documentguide to a feed roll pair and belt. The belt advances the document toplaten 30. After imaging, the original document is fed from platen 30 bythe belt into a guide and feed roll pair. The document then advancesinto an inverter mechanism and back to the document stack through thefeed roll pair. A position gate is provided to divert the document tothe inverter or to the feed roll pair. Imaging of a document is achievedby lamps 32 which illuminate the document on platen 30. Light raysreflected from the document are transmitted through lens 34. Lens 34focuses light images of the original document onto the charged portionof photoconductive surface 12 of belt 10 to selectively dissipate thecharge thereon. This records an electrostatic latent image onphotoconductive surface 12 which corresponds to the informational areacontained within the original document. Thereafter, belt 10 advances theelectrostatic latent image recorded on photoconductive surface 12 todevelopment station C.

At development station C, a pair of magnetic brush developer rollsindicated generally by the reference numerals 36 and 38, advancedeveloper material into contact with the electrostatic latent image. Thelatent image attracts toner particles from the carrier granules of thedeveloper material to form a toner powder image on photoconductivesurface 12 of belt 10. Belt 10 then advances the toner image to transferstation D.

At transfer station D, a copy sheet is moved into contact with the tonerpowder image. Transfer station D includes a corona generating device 40which sprays ions onto the backside of the copy sheet. This attracts thetoner powder image from photoconductive surface 12. After transfer,conveyor 42 advances the copy sheet to fusing station E.

Fusing station E includes a fuser assembly, indicated generally by thereference numeral 44 which permanently affixes the transferred tonerpowder image to the copy sheet. Preferably, fuser assembly 44 includes aheated fuser roller 46 and a back-up roller 48 with the powder image onthe copy sheet contacting fuser roller 46. In this manner, the powderimage is permanently affixed to the copy sheet.

After fusing, the copy sheets are fed to gate 50 which functions, as aninverter selector. Depending upon the position of gate 50, the copysheets are deflected to sheet inverter 52 or bypass inverter 52 and arefed directly to a second decision gate 54. At gate 54, the sheet is in aface-up orientation with the image side, which has been fused, face up.If inverter path 52 is selected, the opposite is true, i.e. the lastprinted side is face down. Decision gate 54 either deflects the sheetdirectly into an output tray 56 or deflects the sheet to decision gate58. Decision gate 58 may divert successive copy sheets to duplexinverter roll 62, or onto a transport path having the sheet transportand registration apparatus of the present invention, indicated generallyby the reference numeral 60. Sheet transport and registration apparatus60 registers and transports successive copy sheets to finishing stationF. At finishing station F, copy sheets are stacked in a compiler trayand attached to one another to form sets. The sheets are attached to oneanother by either a binding device or a stapling device. In either case,a plurality of sets of documents are formed in finishing station F. Whendecision gate 58 diverts the sheet onto inverter roll 62, roll 62inverts and stacks the sheets to be duplexed in duplex tray 64. Duplextray 64 provides an intermediate or buffer storage for those sheets thathave printed on one side and on which an image will be subsequentlyprinted on the second, opposed side thereof, i.e. the sheets beingduplexed. The sheets are stacked in duplex tray face down on top of oneanother in the order in which they are copied.

In order to complete duplex copying, the simplex sheets in tray 64 arefed, in seriatim, by bottom feeder 66 from tray 64 back to transferstation D via conveyors 68 and rollers 70 for transfer of the tonerpowder image to the opposed sides of the copy sheets. Inasmuch assuccessive bottom sheets are fed from duplex tray 64, the proper orclean side of the copy sheet is positioned in contact with belt 10 attransfer station D so that the toner powder image is transferredthereto. The duplex sheet is then fed through the same path as thesimplex sheet to be stacked in tray 56 or, when the finishing operationis selected, to be advanced by sheet transporting and registeringapparatus 60 to finishing station F.

Invariably, after the copy sheet is separated from photoconductivesurface 12 of belt 10, some residual particles remain adhering thereto.These residual particles are removed from photoconductive surface 12 atcleaning station G. Cleaning station G includes a rotatably mountedfibrous or electrostatic brush 72 in contact with photoconductivesurface 12 of belt 10. The particles are cleaned from photoconductivesurface 12 of belt 10 by the rotation of brush 72 in contact therewith.Subsequent to cleaning a discharge lamp (not shown) floodsphotoconductive surface 12 to dissipate any residual electrostaticcharge remaining thereon prior to the charging thereof for the nextsuccessive imaging cycle.

The various machine functions are regulated by a controller 74.Controller 74 is preferably a programmable microprocessor which controlsall of the machine functions hereinbefore described. The controllerprovides a comparison count of the copy sheets, the number of documentsbeing recirculated, the number of copy sheets selected by the operator,time delays, jam corrections, etc. The control of all of the exemplarysystems heretofore described may be accomplished by conventional controlswitch inputs from the printing machine consoles selected by theoperator. Conventional sheet path sensors or switches may be utilized tokeep track of the position of the documents and the copy sheets. Inaddition, controller 74 regulates the various positions of the decisiongates depending upon the mode of operation selected. Thus, when theoperator selects the finishing mode, either an adhesive bindingapparatus and/or a stapling apparatus will be be energized and thedecision gates will be oriented so as to advance either the simplex orduplex copy sheets to sheet transporting and registering apparatus 60,which, in turn transports the copy sheet to the compiler tray atfinishing station F. The detailed operation of sheet transporting andregistering apparatus 60 will be described hereinafter with reference toFIGS. 2 through 4, inclusive.

Referring now to FIG. 2, the features of sheet transporting andregistering apparatus 60 will be described in greater detail. As shownthereat, sheet transporting and registering apparatus 60 includes idlerroller pairs 76 and 78. Each idler pair comprises two idler rollersmounted on a common shaft and spaced from one another to define a gaptherebetween. The idler roller pairs are positioned in slots 80 and 82,respectively, in tray 84. Idler roller pairs 76 and 78 are spaced fromone another and connected to one another by a spring 86. Spring 86resiliently urges idler roller pairs 76 and 78 in a downwardlydirection. Idler roller pairs 76 and 78 are skewed so that thelongitudinal axis of their respective drive shafts is at a transverseangle with respect to registration edge 88 mounted on the side of tray84 and extending in a plane substantially normal to the plane defined bytray 84. Drive rollers 90 and 92 are positioned on the opposed side oftray 84 and are adapted to pass through slots 94 and 96 therein so as tobe located in the gap between their respective idler rollers. Thus,drive roller 92 is located in the gap between the spaced idler rollersof idler roller pair 78 and drive roller 90 is located in the gapbetween adjacent spaced rollers of idler roller pair 76. The foregoingis shown more clearly in FIG. 3. Drive rollers 90 and 92 are spaced fromone another and connected to one another by a timing belt 98. A motor(not shown) rotates the timing belt which, in turn, rotates both driverollers.

Turning now to FIG. 3, there is shown a fragmentary, sectionalelevational view taken along the line 3--3 of FIG. 2 in the direction ofthe arrows. Idler rollers 76 define gap 100. Idler rollers 76 passthrough slots 80 in tray 84. Drive roller 90 passes through slot 94 intray 84 and is positioned in gap 100 between each of the idler rollers.Drive roller 90 is spaced from idler rollers 76. Idler rollers 76 anddrive roller 94 are skewed so as to move copy sheet 102 in a forwarddirection and in a lateral direction. As copy sheet 102 moves in alateral direction, the side edge 104 thereof is moved into contact withregistration edge 88 of tray 84. This aligns the copy sheet. As the copysheet passes beneath idler rollers 76 and above drive roller 90, acorrugation 106 is formed therein. Inasmuch as rollers 76 are spacedfrom drive roller 90, the copy sheet does not pass through a positivenip. Thus, the drive force necessary to move the copy sheet is generatedby the corrugation or bend formed therein. The magnitude of the bend isdependent upon the copy sheet stiffness. As light weight copy sheets arefed through gap 100 and are bent or corrugated, inasmuch as the beamstrength of the copy sheet is relatively low, the copy sheet follows thecontours of the drive roller and idler roller pairs easily. This resultsin a low drive force. In contradistinction, when a heavy weight copysheet is fed through gap 100, inasmuch as the beam strength of the copysheet is relatively high, a high normal force is produced resulting in ahigher driving force on the copy sheet. Spring loading of idler rollers76 reduces the drive force on the heavy weight copy sheets and allows alarger bend or corrugation, and thus a larger drive force, for lighterweight sheets, while not too much bend or corrugation to damage theheavier weight sheets. Thus, as the copy sheet follows the contours ofthe rolls, it first bends, and then straightens as it is released. Asthe copy sheet is released, it moves in a forward direction and in asidewise or lateral direction. Light weight and heavy weight copy sheetsflex at different rates due to their differing beam strengths and thusreceive the necessary force to be advanced without any adjustment. It isclear that the normal force or the drive force on each copy sheet isdependent upon the beam strength or relative thickness of the copysheet. In this way, each copy sheet is driven with the optimum driveforce. Furthermore, when the side edge of the copy sheet engages theregistration edge of the tray, the copy sheet will slip rather thanbuckle. The force required to slip also varies as a function of the thethickness of the copy sheet inasmuch as the normal force varies as afunction of the copy sheet thickness and the slip force is merely africtional force produced by the poduct of the coefficient of frictionand the normal force. Since the normal force is relatively low, theforce required to induce slip of the copy sheet is less than the forcerequired to induce buckling. Hence, as the side edge of the copy sheetengages registration edge 88, the copy sheet will slip in a lateraldirection before buckling.

Referring now to FIG. 4, there is shown a fragmentary, plan view ofsheet transporting and registering apparatus 60 of the presentinvention. As shown thereat, idler rollers 78 are mounted on shaft 106.The longitudinal axis of shaft 106 extends in a direction transverse tothe plane defined by registration edge 88. Thus, idler rollers 78 areskewed, i.e. from an acute angle, with respect to registration edge 88.Drive roller 92 is mounted on its own drive shaft which is similarlyskewed with respect to registration edge 88. Idler rollers 78 passthrough slots 82 in tray 84. Similarly, drive roller 92 passes throughslot 96 in tray 84, idler roller pairs 76 are mounted on shaft 108. Thelongitudinal axis of shaft 108 also extends in a direction substantiallytransverse to the plane defined by registration edge 88. In this way,idler rollers 76 are skewed, i.e. form an acute angle, with respect toregistration edge 88, idler rollers 76 pass through slots 80 in tray 84.Drive roller 90 is mounted on its own drive shafts, the longitudinalaxis of which also extends in a direction substantially transverse tothe plane defined by registration edge 88. Thus, drive roller 90 is alsoskewed with respect to registration edge 88. The longitudinal axis ofthe shafts supporting the drive rollers and the idler rolls aresubstantially parallel to one another. The copy sheet is advanced alonga path of travel in the direction of arrow 110. This path of travel hasa forward component of movement and a lateral component of movement. Asthe copy sheet moves in a lateral direction the side edge thereofengages registration edge 88. When the copy sheet side engagesregistration edge 88, the copy sheet slips in lateral direction whilecontinuing to move in the forward direction. This prevents buckling ofthe copy sheet and damage thereto.

In recapitulation, the sheet transporting and registering apparatusincludes a pair of idler rollers mounted on a common shaft and spacedfrom one another to define a gap therebetween. A drive roller is mountedbetween the idler rollers with portion thereof extending into the gap.The drive roller is spaced from the idler rollers. The copy sheet ismoved over the drive roller and beneath the idler rollers to form a bendor corrugation therein. Thus, as the copy sheet follow the contours ofthe drive roller and idler rollers it first bends and then straightensas it is released. In this way, as the copy sheet straightens, it ispushed in a forward and in a lateral direction. As the copy sheet movesin a lateral direction, the side edge thereof engages the registrationedge. When the copy sheet engages the registration edge, it slips in thelateral direction while continuing to move in the forward direction.This prevents buckling of the copy sheet and damage thereto. Theapparatus of the present invention provides a normal force which variesat different rates inasmuch as it is dependent upon the beam strength ofthe copy sheet, which, in turn, is a function of the thickness thereof.Hence, light weight copy sheets and heavy weight copy sheets deflect atdifferent rates and thus receive the optimum force necessary to advanceeach in both the forward and lateral direction.

It is, therefore, evident that there has been provided, in accordancewith the present invention, an apparatus for moving and aligning copysheets. This apparatus fully satisfies the aims and advantageshereinbefore set forth. While this invention has been described inconjunction with a preferred embodiment thereof, it is evident that manyalternatives, modifications, and variations will be apparent to thoseskilled in the art. Accordingly, it is intended to embrace all suchalternatives, modifications and variations as fall within the spirit andbroad scope of the appended claims.

We claim:
 1. An electrophotographic printing machine of the type havinga document handling apparatus for advancing individual document sheetsfrom a stack to an exposure station and for returning the documentsheets to the stack in repeated cycles, a processor for forming copiesof the documents, and a copy sheet attaching station with each copysheet being aligned during the movement thereof to the sheet attachingstation, wherein the improvement includes:a registration edge; a pair ofidler rollers spaced from one another to define a gap therebetween; adrive roller spaced from said pair of idler rollers and having a portionthereof interposed between said pair of idler rollers in the gap withthe copy sheet passing through the gap having one surface thereofcontacting said pair of idler rollers and the other surface thereofcontacting said drive roller so to bend the copy sheet in the gap, saiddrive roller and said pair of idler rollers having their respectivelongitudinal axes substantially parallel to one another and extending ina direction transverse to said registration edge; and means forresiliently urging said pair of idler rollers into contact with the copysheet sheet, said drive roller and said pair of idler rollers moving thecopy sheet along a path having a forward direction of movement and alateral direction of movement substantially normal to the forwarddirection with the lateral movement of the copy sheet causing the sideedge of the copy sheet to engage said registration edge so as to bealigned thereat, said drive roller and said pair of idler rollersapplying a moving force having a magnitude proportional to the thicknessof the copy sheet so that the moving force varies as a function of thethickness of the copy sheet being moved with the copy sheet slippinglaterally when engaging said registration edge to prevent bucklingthereof. .Iadd.
 2. An electrophotographic printing machine of the typein which an original document is reproduced on a copy sheet, wherein theimprovement for aligning each copy sheet includes:a registration edge; apair of idler rollers spaced from one another to define a gaptherebetween; a drive roller spaced from said pair of idler rollers andhaving a portion thereof interposed between said pair of idler rollersin the gap with the copy sheet passing through the gap having onesurface thereof contacting said pair of idler rollers and the othersurface thereof contacting said drive roller so as to bend the copysheet in the gap, said drive roller and said pair of idler rollershaving their respective longitudinal axes substantially parallel to oneanother and extending in a direction transverse to said registrationedge; and means for resiliently urging said pair of idler rollers intocontact with the copy sheet, said drive roller and said pair of idlerrollers moving the copy sheet along a path having a forward direction ofmovement and a lateral direction of movement substantially normal to theforward direction with the lateral movement of the copy sheet causingthe side edge of the copy sheet to engage said registration edge so asto be aligned thereat, said drive roller and said pair of idler rollersapplying a moving force having a magnitude proportional to the thicknessof the copy sheet so that the moving force varies as a function of thethickness of the copy sheet being moved with the copy sheet slippinglaterally when engaging said registration edge to prevent bucklingthereof. .Iaddend.